I believe that you are mixing two aspects of IANA. There is the part that does ccTLD delegations - which is a highly intensive, very political, very subjective, and time consuming task.

Then there is the part of simply assigning protocol numbers and similar things (such as putting certain names onto lists of known mime and media types.)

It is that latter function that the IAB seems to be complaining about.

That latter function is strongly structured and for much of the work is relatively easily handled by predictable, non-discretionary and predictable procedures. And because most of the protocol assingment tasks are independent of one another they can be handled in parallal - more people can lead to more completed work.

Given ICANN's ever expanding cost to the internet the IAB does seem to have a very valid concern about why one of ICANN's necessary and primary jobs seems to be getting second-class treatment while ICANN's non-necessary job of rolling out the red carpet for the intellectual property community gets first class treatment.